1. Field of the invention
This invention relates to the analysis and evaluation of the results of ultrasonic examinations of solid objects by the pulse-echo method. The correct location, interpretation and sizing of internal flaws in materials and welded joints are matters of the greatest importance for the safety and fitness for purpose of important structures and installations.
2. Background of the Prior Art
In the ultrasonic examination art, great efforts have been made to develop improved systems for the location and sizing of flaws in materials and welded joints, in particular systems producing easily readable images of internal flaws. In many systems this has been made possible through the use of digital computing means including electronic matrix memories for the storage of echo data which may then be analysed, displayed on video monitors as grey scale or colour images, and permanently recorded by magnetic recording means or permanent prints.
In two previous patent applications, WO Lund et al. 87/07026, and U.S. Lund et al. Ser. No. 223,014, filed Apr. 1988 we have disclosed systems and methods of ultrasonic examination providing sectional and projection views showing flaw images of greatly improved precision and sharpness of definition.
According to said previous inventions, at least one ultrasonic probe is moved over the surface of the object examined, transmitting, at predetermined intervals of time, at least one short pulse of ultrasonic energy into the object. Signals containing information on the points of incidence of the sound beam, on the directions of the central axis of the sound beam, on the amplitudes of echo pulses from inhomogeneities, and on the corresponding path lengths of the sound beam, are measured, digitalised, stored and used to create video sectional and projection views showing clear and sharp images of inhomogeneities inside the object. Such images may then be permanently recorded and printed in grey scale and colours for display, analysis and evaluation at any later time. The systems according to said previous inventions have, in practical examinations, led to a drastic increase in the quality and precision of sectional and projection images, permitting a correct and precise location and evaluation of all inhomogeneities in three dimensions.
One problem has, however, remained to be solved. When a sound pulse is transmitted into the material and reflected from an inhomogeneity, the sound may travel along several different paths and undergo mode conversion on its way to and from the inhomogeneity. This fact leads to the formation of multiple images of one and the same inhomogeneity, and to `ghost images` due to reflections from other inhomogeneities. It is then a cumbersome and time consuming task to keep track of and evaluate or eliminate such echoes, before a final decision can be made on the correct interpretation of the results of the examination.